The global presence of plastic debris has become an indisputable environmental issue. While it is useful to recycle used plastic materials, contaminated plastics require a series of pretreatments prior to the process. Here, we offer a viable thermochemical conversion (pyrolysis) platform to directly valorize fishing net waste (FNW). Prior to the pyrolysis of FNW that was collected at a Korean seaport, its chemical composition (polyethylene) was examined using thermogravimetric analysis, ultimate analysis, and Fourier-transform infrared spectroscopy measurements. Pyrolysis of FNW was conducted to produce value-added syngas and C1-2 hydrocarbons (HCs) in both CO2 and N-2 environments with a variety of pyrolysis setups. The pyrolysis temperature significantly contributed to the thermal cracking of long-chain liquid HCs into H-2 and C1-2 HCs under the N-2 and CO2 conditions. In the presence of cobalt-based catalysts, an additional improvement of the reaction kinetics for producing H-2 and C1-2 HCs was shown in the N-2 environment. However, the synergistic effectiveness of Co-based catalysts and CO2 resulted in CO formation, because CO2 provided additional C and O sources over the Co-based catalysts. Thus, it allowed control of the H-2/CO ratio in the CO2 and N-2 atmospheres. The compositional matrix of the liquid HCs after pyrolysis also confirmed that CO2 controlled their aromaticity. Thus, the CO2-cofeeding pyrolysis of FNW can be considered a viable platform for the direct treatment of plastic wastes by harvesting energy as a form of syngas.